Martha Casquete
Newton s Third Law of Motion Newton s Law of Gravitation Buoyancy Momentum 3-2 Section 3.4
Net force/balance and unbalance forces Newton s First Law of Motion/Law of Inertia Newton s Second Law of Motion/ F = ma 3-3 Section 3.4
When more than one force acts, a net, or unbalanced, force is need A single applied force will produce an acceleration How much inertia do you have? Newton s First Law of Motion is sometimes called the law of inertia According to Newton s second law, an external, net force will produce an acceleration 3-4 Section 3.4
Mass = amount of matter present Weight =related to the force of gravity Earth: weight = mass x acc. due to gravity w = mg (special case of F = ma) Weight is a force due to the pull of gravity. Therefore, one s weight changes due to changing pull of gravity like between the earth and moon. Moon s gravity is only 1/6 th that of earth s. 3-5 Section 3.3
What is the weight of a 3.50 kg mass on (a) earth, and (b) the moon? (in N and lb) 1 lb = 4.45 N 3-6 Section 3.3
Both are doubled! 3-7 Section 3.3
It is the ever-present resistance to relative motion that occurs whenever two materials are in contact with each other. Classified into two types: static friction and sliding (or kinetic). Static friction occurs when the frictional force is sufficient to prevent relative motion between surfaces. Sliding friction, or kinetic friction, occurs when there is relative (sliding) motion between the surfaces in contact. Static friction larger than sliding friction 3-8 Section 3.4
For every action there is an equal and opposite reaction. or Whenever on object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. action = opposite reaction F 1 = -F 2 or m 1 a 1 = -m 2 a 2 3-9 Section 3.4
F 1 = -F 2 or m 1 a 1 = -m 2 a 2 Jet propulsion exhaust gases in one direction and the rocket in the other direction Gravity jump from a table and you will accelerate to earth. In reality BOTH you and the earth are accelerating towards each other You small mass, huge acceleration (m 1 a 1 ) Earth huge mass, very small acceleration (-m 2 a 2 ) BUT m 1 a 1 = -m 2 a 2 3-11 Section 3.4
Friction on the tires provides necessary centripetal acceleration. Passengers continue straight ahead in original direction and as car turns the door comes toward passenger 1 st Law As car turns you push against door and the door equally pushes against you 3 rd Law 3-12 Section 3.4
What keeps the Moon in orbit around the Earth? Are astronauts seen floating in the international Space Station really weightless? 3-13 Section 3.5
Gravity is a fundamental force of nature We do not know what causes it We can only describe it Law of Universal Gravitation Every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them 3-14 Section 3.5
Gm 1 m 2 Equation form: F = G is the universal gravitational constant G = 6.67 x 10-11 N. m 2 /kg 2 G: is a very small quantity thought to be valid throughout the universe was measured by Cavendish 70 years after Newton s death not equal to g and not a force r 2 3-15 Section 3.5
The forces that attract particles together are equal and opposite F 1 = -F 2 or m 1 a 1 = -m 2 a 2 3-16 Section 3.5
F = Gm 1 m 2 r 2 For a homogeneous sphere the gravitational force acts as if all the mass of the sphere were at its center 3-17 Section 3.5
Example: Two objects with masses of 2.5 kg and 3.0 kg are 2.0 m apart. What is the force in each mass in Newtons and pounds? What is the magnitude of the gravitational force between the masses? 3-18 Section 3.5
GmM E F = R 2 [force of gravity on object of mass m] E M E and R E are the mass and radius of Earth This force is just the object s weight (w = mg) \ w = mg = G mme R E 2 GM E g = R 2 E m cancels out \ g is independent of mass 3-19 Section 3.5
g = GM r 2 g = acceleration due to gravity M = mass of any spherical uniform object r = distance from the object s center 3-20 Section 3.5
1) Proper Tangential Velocity 2) Centripetal Force F c = ma c = mv 2 /r (since a c = v 2 /r) The proper combination will keep the moon or an artificial satellite in stable orbit 3-21 Section 3.5
3-22 Section 3.5
Linear momentum = mass x velocity p= mv If we have a system of masses, the linear momentum is the sum of all individual momentum vectors. P f = P i (final = initial) P = r 1 + r 2 + r 3 + (sum of the individual momentum vectors) 3-23 Section 365
Law of Conservation of Linear Momentum - the total linear momentum of an isolated system remains the same if there is no external, unbalanced force acting on the system Linear Momentum is conserved as long as there are no external unbalance forces. It does not change with time. 3-24 Section 3.6
P i = P f = 0 (for man and boat) When the man jumps out of the boat he has momentum in one direction and, therefore, so does the boat. Their momentums must cancel out! (= 0) 3-25 Section 3.6
How Newton s three laws, momentum and impulse have to do with a car accident? What can we learn from a raw egg? 3-26 Section 3.6
First, I need to explain what impulse is: Start with Newton s Second Law F = m a but a = v/t Hence, F = m (v/t) what happens if we mult. by t F * t = m * v Well, in physics F* t = Impulse and m* v = momentum Therefore: change impulse = change momentum 3-27 Section 3.6
3-28 Section 3.6
Egg
F = ma (2 nd Law) or w = mg (for weight) F 1 = -F 2 (3 rd Law) F = (Gm 1 m 2 )/r 2 (Law of Gravitation) G = 6.67 x 10-11 N-m 2 /kg 2 (gravitational constant) g = GM/r 2 (acc. of gravity, M=mass of sph. object) P = mv (linear momentum) P f = P i (conservation of linear momentum) Impulse = F * t = change in momentum 3-30